# -*- coding: utf-8 -*-
"""
Created on Fri Sep 18 11:31:20 2020

@author: Administrator
"""

'''

You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).

You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.

 

Example 1:


Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
Output: [[7,4,1],[8,5,2],[9,6,3]]
Example 2:


Input: matrix = [[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]]
Output: [[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]]
Example 3:

Input: matrix = [[1]]
Output: [[1]]
Example 4:

Input: matrix = [[1,2],[3,4]]
Output: [[3,1],[4,2]]
 

Constraints:

matrix.length == n
matrix[i].length == n
1 <= n <= 20
-1000 <= matrix[i][j] <= 1000

'''

class Solution:
    def rotate(self, matrix: List[List[int]]) -> None:
        """
        Do not return anything, modify matrix in-place instead.
        """
        '''
        20200917--李运辰
        不熟悉
        
        0,0 0,1 0,2
        1,0 1,1 1,2
        2,0 2,1 2,2
        
        2,0 1,0 0,0
        2,1 1,1 0,1
        2,2 1,2 0,2
        '''
        
        
        '''
        l=0 1
        r=2 1

        0,0 0,1 0,2
        1,0 1,1 1,2
        2,0 2,1 2,2

        2,0 2,1 2,2
        1,0 1,1 1,2
        0,0 0,1 0,2

        i=0
        j=0
        2,0 2,1 2,2
        1,0 1,1 1,2
        0,0 0,1 0,2

        i=1
        j=0


        2,0 1,0 0,0
        2,1 1,1 0,1
        2,2 1,2 0,2
        '''
        l=0
        r=len(matrix)-1
        
        while l<r:
            #这里l和r有先后关系？？   没有关系
            matrix[r],matrix[l] = matrix[l],matrix[r]
            l +=1
            r -=1
            
        for i in range(len(matrix)):
            for j in range(i):
                #这里i和j有先后关系？？   没有关系
                matrix[j][i],matrix[i][j] = matrix[i][j],matrix[j][i]
                
        
                
            